1. Field of the Invention
The present invention relates to a method for controlling and balancing the power consumption in an electric smelting or a heating furnace, in which power is fed into the furnace via at least two electrodes and at the early stage equilibrium is established by moving the electrodes.
2. Description of the Prior Art
U.S. Pat. No. 4,296,269 of Stewart et al substantially corresponding to ZA Patent Application No. 773923 discloses an electric furnace control system which is based on the observation of the states present in the secondary circuit. In accordance with the system, selected values of the primary and the secondary circuits are measured and the results of the measurement are computer processed. The computer processing enhances the control of the furnace in such a way that the behavior of the inductances of the secondary circuits can be predicted on the basis of other changes occurring in the furnace. The obtained computer values are further applied to the furnace control devices in such a way that the conditions in the furnace can be maintained within predetermined limits by moving the electrodes, when necessary, either downwards or upwards.
The practical implementation of the control system according to U.S. Pat. No. 4,296,269 and ZA Patent Application No. 773923 requires that the secondary circuit inductances are predictable and maintained equal to each other and that, when using these inductance values, the determined resistance values are to be compared with predetermined approximate resistance values. In this case, since the power transmitted by the electrodes is greatly dependent on the resistance values used, which in the system according to U.S. Pat. No. 4,296,269 ZA Patent Application No. 773923 are largely dependent on the predetermined values, adjustments of the power required by the furnace are effected by moving the electrodes either downwards or upwards.
The power control of an electric furnace carried out by moving the electrodes is disadvantageous as regards the electrodes, since the electrodes are thereby subjected to great variations of temperature, among other things. When self-sintering co-called Soderberg electrodes are used, the distribution of temperature is crucial for the operation of an electrode. The Soderberg electrode paste is prepared by mixing a carbon-containing material and a tar-pitch bonding agent. Qualitatively the properties of the paste can be distributed into two parts, the upper side and the lower side of the sintering zone. The lower, sintered part can be regarded as a complete electrode, in which the physical properties of the solid carbon material are important considering the operation of the electrode. In the upper part the main requirement for the paste is good fluidity, since it is important that the paste flows at a moderate temperature and fills the mantle properly. In this case it is important with regard to the whole electrode to maintain both the level of the molten paste and the sintering zone within certain limits. The levels of these zones are primarily affected by the temperature. As regards the operation of the electrode, disadvantageous heights may cause problems, even the breaking of the electrodes into two.